1. Field of the Invention
The present invention relates to a lens for reading an original and effectively utilized to especially read a color original.
2. Description of the Related Art
In a general digital color copying machine, etc., a color original is read by decomposing a color thereof into three primary colors composed of red, green and blue.
In such a reading operation of the color original, there is a known method for reading an original image of each of the decomposed colors on the same plane.
In this method, for example, a solid-state image sensor is arranged such that a position of this sensor is in conformity with an image forming face formed by a lens for reading the color original. Filters for color decomposition are switched between the original reading lens and the solid-state image sensor.
Recently, a solid-state image sensor for only a color image has been practically used. This sensor has three lines of light-receiving elements and also has red, green and blue filters arranged every line. The original image of each of the decomposed colors is simultaneously read on the same plane by using this solid-state image sensor.
As mentioned above, when the original image of each of the decomposed colors with respect to the color original is read on the same plane, it is necessary to construct the lens for reading the original such that best focusing faces with respect to the red, green and blue light colors are effectively in conformity with each other.
In general, there is no known lens for reading an original constructed such that the best focusing faces with respect to the red, green and blue light colors are effectively in conformity with each other when this lens is used at a reduced magnification.